Regarding that spectific part, I've decided it's because he speaks German and it's a language use to tame animals in circuses and, I'm my country anyway, used to train difficult dogs. And well, technically, Parrish is a dog of some sorts so voilà, I've decided randomly that it was the reason and I stand by it!
To explain the fact that the team is remembering people: wasn't there a moment during the attack in the lacrosse field, when Invisible Boy (I never remember the name of the newbies) touched all of them and after that, they could see the riders too? Isn't that linked with the moment in the library when he makes a library card (?) "reappear" for his boyfriend to see? I might be mistaken because when it's not the parents, I'm not following very closely I must confess. But if that really happened, I think their abilities to see/remembers is linked to previous actions from Invisble Boy. If that's not it because those scenes didn't happen like I remember and understood them... well, sorry to have wasted your time with a completly wrong explanation!
And speaking of the parents, that 39 years old woman shamelessly bawled her eyes out during the Sheriff scenes remembering his son and letting his wife go. That got to me hard! This was really beautifully done, very touching without being over the top drama 101.